1) Field of the Invention
This invention pertains to the field of liquid crystal display (LCD) devices, such as liquid crystal on silicon (LCOS) devices, and more particularly to a structure for such a device providing for uniform spacers.
2) Description of the Related Art
Reflective LCD devices are well known. Examples of such devices, and in particular active matrix devices, are shown in U.S. Pat. Nos. 6,023,309 and 6,052,165. With reference to the following description, familiarity with conventional features of such devices will be assumed, so that only features bearing on the present invention will be described.
FIG. 1 shows a portion of a typical prior-art reflective LCD device 100. The reflective LCD device 100 may generally be divided into a pixel region 100a (active region) and a peripheral region 100b. The pixel region 100a includes an array of pixel elements and the peripheral region 100b includes driver circuits 105 for supplying driving signals to each of the pixel elements.
The LCD device 100 comprises, in relevant part, a silicon substrate 110, an insulating layer 112, a liquid crystal layer 114, a transparent electrode 116, such as indium-tin-oxide (ITO), and a transparent (e.g., glass) layer 118. A reflective mirror (pixel) metal layer 120 is provided beneath the liquid crystal layer 114 on the insulating layer 112. The mirror metal layer 120 includes a plurality of individual reflective pixel electrodes 120a in the pixel region 100a, and a substantially continuous peripheral portion 120b formed in the peripheral region 100b of the LCD device 200. Light transmissive regions 122 are located between the pixel electrodes 120a. 
Also provided in the insulating layer 112 and between the mirror metal layer 120 and the substrate 110 are a light shield metal layer 124 and routing metal layers, 128 and 130. In the pixel region 100a, the metal layers 128 and 130 form mutually-orthogonal row and column lines, which may be connected to gate and source electrodes of MOS transistors (not shown in FIG. 1) for pixel elements fabricated in the underlying substrate 110. In the peripheral region 100b, the metal layers 128 and 130 form signal routing lines used for routing various signals of the driver circuits. Also, metal plugs or vias 132 are provided for connecting various portions of the light shield metal layer 124 and the third and fourth metal layers 128, 130 with each other.
The metal layer 124 is provided to prevent light entering the device, such as through the transmissive regions 122 between the pixel electrodes 120a, from reaching the substrate 110 where it might induce leakage currents on otherwise interfere with proper device operation. While portions of metal layers 128 or 130 may incidentally block a small portion of light entering the device, the structure of FIG. 1 requires a separate metal layer 124 to be dedicated to provide the required degree of light blocking in the peripheral region 100b. 
A plurality of spacers or pillars are provided for supporting the transparent layer 118 and providing a gap for the liquid crystal layer 114. In the pixel region 100a, the spacers 134a are placed directly on the insulating layer 112. In the peripheral region 100b, spacers 134b are provided on the peripheral portion 120b of the mirror metal layer 120.
In order to maintain a uniform liquid crystal cell gap, it becomes necessary for the spacers in the peripheral region 100b to have a height that is the same as the spacers in the pixel region 100a. However, the spacers 134b formed on the mirror metal layer 120 in the peripheral region 100b are taller than the spacers 134a formed on the insulating layer 112 in the pixel region 100a because of the extra height of the metal layer 120, thus producing a non-uniform display.
Accordingly, it would be desirable to provide a liquid crystal display device having spacers with a more uniform height in both the pixel and peripheral regions of a reflective LCD device. Other and further objects and advantages will appear hereinafter.
It is therefore an object of the invention to provide a liquid crystal display (LCD) device having a more uniform spacer structure.
In accordance with one aspect of the invention, an LCD device is provided having a pixel region and a peripheral region adjacent to the pixel region, comprising a silicon substrate, an insulating layer on the substrate, a first metal layer above the insulating layer including an array of pixel electrodes in the pixel region and a peripheral portion in the peripheral region having a plurality of openings therein, a plurality of spacers in the openings, a second metal layer between the first metal layer and the substrate, and a plurality of walls each corresponding to one of the plurality of openings and extending substantially between the second metal layer and the first metal layer.